1.Field of the Invention
The present invention relates to an apparatus for polishing-grinding a semiconductor wafer.
More particularly, this invention relates to an apparatus for grinding a semiconductor wafer which can easily remove dusts produced by the grinding process.
2. Description of Related Art
In general, semiconductor wafers are obtained from silicon ingots by slicing, grinding, chemical etching, and polishing. Grinding processes are classified into single-side grinding and dual-side grinding. The single-side grinding method is used to grind a backside of semiconductor wafers so that the wafer are in a suitable condition for gold deposition and assembly. By grinding the backside of semiconductor wafers, unnecessary films on the wafers can be controlled so as to be suitable for subsequent processing. According to this grinding process, a mixture of an abrasive and a lapping vehicle is put between a lapping plate and the semiconductor wafer, and then a rubbing force is applied to the wafer. The lapping plate and wafer are polished by the action of the abrasive and the lapping vehicle so that the surface of the wafer is smoothed.
It is particularly important in the grinding process to minimize the generation of dust contaminants. For example, during the slicing process or the grinding process, particulate dust, including abrasive material, iron, crushed silicon, etc. is created. Such dust negatively affects the gold deposition process. Therefore, the surface of the wafer should be smoothed while also removing such dust, and the surface of the crystalline silicon should be cleansed by removing contaminants from the crystalline silicon surface. A washing process in the semiconductor fabrication process is also important. By using a washing process, adhesives used in the grinding process, photosensitive films for protecting a front surface of a wafer, and any other unnecessary or undesirable elements can be removed.
Referring the accompanied drawings, FIGS. 1(A), 1(B), and 2 illustrate a known apparatus for grinding a backside of semiconduct wafers.
FIG. 1A is a view of a conventional apparatus for grinding semiconductor wafers. FIG. 1B illustrates a condition in which silicon and other dusts are transmitted to an edge side of the view of a wafer-cleaning part of a conventional polishing apparatus.
The conventional wafer-grinding apparatus is described hereinbelow.
A chemical/mechanical grinding step is used to produce a highly reflective surface without scratches or other damages on one side of a semiconductor wafer. According to a conventional grinding process for grinding a wafer 3, a wafer 3 having a frontside thereof covered with a protective tape is put, frontside down, on a vacuum chuck table 2. The backside of the wafer 3 is polished by a grinding wheel 1 which has a known thickness. If the wafer 3 has a proper thickness and surface, the tape of the front side of the wafer 3 may be removed. During the above-described grinding process, silicon and other dusts 102 (represented by radiating arrows in FIG. 1A) are produced. Since the dust 102 prevents proper polishing of the surface of the wafer 3, dust 102 must be removed.
As shown in FIG. 1A, the conventional grinding apparatus uses a water jet 101 during grinding. After the grinding step, the conventional apparatus cleans dust 102 and then dries the wet wafer. In addition, water jet 101 flows water from the grinding wheel 1 to the side if the wafer 3 being polished, so dust 102 is carried in the stream of water 101 from the center portion of the wafer 3 to the edge thereof, as seen at 103 in FIG. 1B.
As shown in FIG. 2, the wafer 3 is then put on a spin chuck table 4 so that the frontside of the wafer 3 is opposite to the spin chuck table 4. Dust from the wafer 3 are entrained in the inflow of water 201. Such an apparatus includes a final drying step.
Only one method for supplying water is typically used to flow washing water in the conventional apparatus. With the inflow of water 101, dust 102 naturally spreads over one side of the wafer 3, and it migrates to the opposite side of the wafer 3 because of the vacuum action of the chuck table 2. Consequently, large amounts of dust tend to migrate to the front-side of the wafer 3, and it is difficult to remove this dust from the frontside. Moreover, washing water 201 only flows over the back-side of the polished wafer 3 in order to clean it. Therefore, dust remains on the frontside of the wafer 3, even though the cleaning process is performed.
In the case of a 6" inch semiconductor wafer, for example, the amount of dust which remains on the frontside of the semiconductor wafer after cleaning step is not usually problematic.
However, since wafers have become larger recently (for example, 8" inches), the amount of resultant remaining dust can increase by two or three times. In addition, a remover tape is used to remove a coating tape which was stuck on the frontside of the wafer before grinding. The remover tape is weakly adhered because of the increased amount of dust on the front of the wafer. After all, it is disadvantageous that the wafer is broken and occurs an error in sticking a remover tape on the coating tape.